Although not an essential nutrient, quercetin is a substance found in some fruits and vegetables that may provide important antioxidant effects. You can take quercetin supplements to help in treating a wide variety of health conditions, such as allergies, heart disease, prostatitis and certain eye conditions. Talk with your healthcare provider before taking quercetin tablets or capsules to discuss proper dosage and any potential health risks or interactions.
Description
Quercetin is a water-soluble substance that gives certain fruits and vegetables their coloring, explains the University of Pittsburgh Medical Center. These plant-based pigments are called bioflavonoids. Quercetin is found in small doses in beans and leafy green vegetables, but in larger amounts in onions, apples, grapefruits, red wine, buckwheat, green tea and black tea.
Benefits
Quercetin supplements may help to treat allergies, inflammation and cardiovascular diseases, as well as potentially prevent and treat cancer, says the Memorial Sloan-Kettering Cancer Center. Quercetin may also help to treat eczema, asthma, hives, prostatitis and interstitial cystitis. Some medical evidence indicates that taking quercetin supplements can help treat cataracts, certain childhood diseases, gout, edema, peptic ulcers, diabetes and retinopathy, notes the University of Michigan Health System. You can take the typical dosage of 200 to 500 mg of quercetin two or three times daily. For therapeutic uses, you must take a supplement, because vegetables and fruits contain only small amounts of quercetin.
Function
Quercetin contains bioflavonoids, which provide the antioxidant properties that help fight free radicals in the body. Quercetin's bioflavonoids also suppress your body's histamine and leukotriene production, which provide the anti-inflammatory actions and allergic reaction-fighting effects. The major constituents in quercetin may also inhibit cholesterol absorption, as well as provide antiviral and anticancer actions.
Medical Evidence
Test tube studies published in the Journal of Allergy and Clinical Immunology in 1985 and in Progress in Clinical and Biological Research in 1986 found that the flavonoids contained in quercetin blocked histamine release and other activities in the body associated with allergic reactions that lead to hives, eczema, asthma and hay fever. Published in the Journal of Science, a 1977 study of rats with diabetes found that quercetin prevented cataract formation. A human double-blind clinical trial published in the Journal of Urology in 1999 revealed that taking quercetin supplements helped treat chronic prostatitis, a condition involving prostate inflammation in men. A 2000 test tube study published in the Alternative Medicine Review also found that quercetin's antioxidant properties may offer anticancer effects. A double-blind clinical trial found that quercetin can help to treat interstitial cystitis symptoms, and the results of this trial were presented at the American Urological Association 2001 Annual Meeting. Finally, two 1985 studies published in the Journal of Medical Virology and the medical journal Experientia revealed that quercetin's flavonoids have antiviral effects on herpes, polio and influenza viruses.
Warnings
If you're pregnant, you shouldn't take quercetin supplements due to the potential risk of infant leukemia and possible chromosomal mutations. Also, if your doctor is conducting a test to diagnose the rare but deadly condition called neuroblastoma, keep in mind that taking quercetin supplements may cause a falsely positive test result due to their effects on homovanillic acid levels in your blood and urine.
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